Upconversion Nanoparticles Capped with Molecularly Imprinted Polymer as Fluorescence Probe for the Determination of Ractopamine in Water and Pork

A novel fluorescence probe was designed and synthesized to quantify ractopamine in foods using molecularly imprinted polymer (MIP) as a specific recognition element and YF 3 :Yb 3+ , Er 3+ upconversion nanoparticles (UCNPs) as a fluorescence signaling component. The developed UCNP@MIP probe was characterized using X-ray powder diffraction, scanning electron microscopy, and thermogravimetric analysis. The fluorescence of UCNP@MIP probe was quenched specifically by ractopamine, and good linear regression ranging from 1.66 × 10 −8 to 3.3 × 10 −7  mol/L was obtained with the limit of detection of 8.6 × 10 −10  mol/L. This method was further applied to determine ractopamine in water and pork samples. Recoveries between 76.61 and 88.97% were obtained with relative standard deviation ranging from 1.15 to 2.67% ( n  = 3). This UCNP@MIP probe combined high selectivity of MIP and high sensitivity of upconversion fluorophore and showed potential to determine various food chemical hazards.